Clem and all other developers - what a magnificent piece of work Linux Mint 19! I did have some difficulties installing it, but actually minor hiccups. As far as I can see, the installation failures were caused by the changes in the good old grub. To be able to work in now needs a small separate partition for the bootloader. Having created the bootloader partiion, which is named "Reserved BIOS boot area" I needed to try several file systems - ext4 worked. This was on my "vdesk" main pc, which now has linux only.
I then tested the installation on an older laptop. I tried the "format the whole disk" option. The "auto" partitioning leaves a partiton for the efi, but no partition for the bootloader. It worked fine in older grub setup, but not now. I tried the mint 18.3 and that worked fine. All that is needed is a revision of the partitioning with a provision of a small partition for the boot loader.
Hope this little experiment will be helpful.
I would be happy and willing to do more testing, if requested. Should I write a message in the bug tracker?
OldAl.

Hello!
I'm running Mint 17.3 Mate 64bit.
I've done backup, and created snapshot with timeshift.
What is the safest way of upgrading to Mint 19 Mate? Do I have to upgrade to Mint 18.3 first? If yes, where is this instruction?

Hello!
I'm running Mint 17.3 Mate 64bit.
I've done backup, and created snapshot with timeshift.
What is the safest way of upgrading to Mint 19 Mate? Do I have to upgrade to Mint 18.3 first? If yes, where is this instruction?

you can't upgrade to 19 from 17, just do a fresh install, and you will like it better.

I'm not a fan. I tried setting it up to do 1 monthly backup & had it store it on my freshly formatted 1 terabyte HD. Started it & HD light never went off, even after 4 hours. Now it was backing up my 480 GB NVME which only had 80 gigs used, but when I looked at the backup storage drive it was down to around 500 gigs left. I'll stick with Clonezilla thank you.

Sounds like you didn't create a filter to exclude your 1 TB HD from the backups, so timeshift would basically create snapshots of the snapshots as well and thus exponentially grow the snapshot sizes. Correctly configured all the timeshift snapshots combined take up little more space than the space used on your root partition.

Yea! I added /Storage/*** to the exclude Patterns Filter list & now it's working. Sorry about the length of time before replying, one day a couple of weeks ago I woke up & my body decided I needed a Pacemaker. Who Knew??? Just now got around to trying it.

Thanks to the Mint team for an issue-free update from 18.3 Cinnamon to 19 Cinnamon....

Here is a sample with output when attempting to execute gparted:
...
Unit -.mount does not exist, proceeding anyway.

I wish that my "update" from 18.3 Cinnamon to 19.0 Cinnamon had gone as smoothly as yours. I spent over a week on several issues, including ownership problems, and the inability to install network printers through normal procedures (procedures that worked in 18.3).

[I didn't "upgrade" via the procedure given in the release documentation, because it seemed far to complicated. Instead, I did a clean install, retaining my home partition and all the settings contained therein, and re-doing the various settings that are contained in the root partition.]

I'm getting the "Unit -.mount does not exist, proceeding anyway." message when gparted is started from a terminal under Linux Mint 19. It doesn't prevent gparted from starting, and it doesn't seem to cause any other problems in gparted's functioning. Note that Mint 18.3 displayed "too few arguments" when "gparted /dev/xxx" was started from the terminal, so this is a change in bugs, but not any worse than before. From the Ubuntu forums, it seems that the "Unit" message is occurring in other Ubuntu 18.04 distributions, along with problems in starting gparted.

Only one fly-in-the-ointment with the upgrade from 18.3 to 19.0, I did not have the locales-all package installed prior to running the mintupgrade command. The installation process complained about not being able to set the locales LC_ALL variable. As a consequence, the dbus-x11 package would not install and the upgrade process halted.

So, word of advice, if your system lacks the locales-all package, install it prior to attempting the upgrade.

If you happen to be in the middle of the upgrade and it halts with errors because of the locales, simply install the locales-all package and then the dbus-x11 package. The apt command will finish the installation of queued up packages. Once all of the installation activity has settled down, simply restart the mintupgrade command.

Any chance to be able to upgrade without the timeshift procedure?
Diskspace's running low for snapshots and fresh install is not an option.

Timeshift is only there to allow you to roll the upgrade back in case something goes wrong. You can skip the timeshift step if you want to take the risk, but with you saying that a fresh install not being an option I'd be very careful with that decision.

Note that timeshift can also backup to an USB stick (once formatted as ext4).

I have to admit, I find the timesheet requirement in mintupgrade to be annoying.

We are Linux users. We don't need to be nannied. Leave that shit for Windows.

I usually do a full disk image to my NAS before I upgrade anyway, so the timeshift requirement is an annoyance. I don't even have timeshift installed, as I find the fact that it can't backup to remote filesystems makes it completely useless.

Now, I'm told I can touch /etc/timeshift.json to override this requirement, but my system doesn't even have that file....

Maybe I'll just do a manual upgrade by manually changing the repositories and doing a dist-upgrade. That ought to do it, right?

We are Linux users. We don't need to be nannied. Leave that shit for Windows.
[,,,]
Now, I'm told I can touch /etc/timeshift.json to override this requirement, but my system doesn't even have that file....

Case in point, the touch command creates a non-existent file, that's why you were told to use it. You were saying?

I probably would have made it optional, too, had I created the upgrade script, but I can see why they opted for a little bit of forced hand-holding instead; better safe than sorry.